Interaction of filamin with epithin and release of epithin are inhibited by the actin-binding-deficient filamin-B. (A) Epithin and histidine (His)-tagged human filamin-B1704−2602 constructs were co-transfected into M2 cells, and the cells were treated with phorbol myristate acetate (PMA) and/or cytochalasin D (CytoD), as indicated. Cell lysates were immunoprecipitated (IP) with anti-N antiserum, and blotted (IB) with anti-His antibody or with anti-N antiserum. (B) M2 cells were transfected with indicated complementary DNAs and treated with PMA. Cell lysates were immunoprecipitated with anti-N antiserum, and blotted with anti-filamin antiserum for filamin-A (upper panel). The amounts of filamin-A and His–filamin-B1704−2602 in the cell lysates are shown (lower panel). (C) Release of endogenous epithin in 427.1.86 cells was examined after transfection of the increasing amounts of His–filamin-B1704−2602 cDNAs, as indicated.